A femto cell is a term obtained by combining a femto, denoting a factor of 10.sup.-15 or 0.000000000000001, and a cell, which refers to a very small mobile communication base station installed indoors such as homes, offices, and the like.
A femto cell is installed in an area in which radiowaves of a macro cell are degraded in a shadow area, like indoor areas, in order to improve a service available area and improve the capacity to increase quality of service (QoS).
FIG. 1 illustrates an architecture of a mobile communication system in which femto cells are installed.
The femto cells are connected to a femto cell controller 103 through a broadband network, and the femto cell controller 103 is connected to a mobile communication core network.
In general, the femto cells have a small number of terminal entities connected to their coverage to receive a service. Thus, when a terminal connected to each femto cell operates in an idle mode or when there is no terminal connected within a femto cell coverage, the femto cells operate in a femto cell idle mode (Femto Cell Low Duty Cycle Mode, 110, 120, 130) in order to prevent unnecessary power consumption. Also, the femto cells may operate in the idle modes 110, 120, and 130 in order to cancel interference between the macro cell and the femto cells or between the femto cells.
For the idle mode operation of the femto cells, an application of an idle mode scheme of general terminals may be taken in consideration; however, because the femto cells are a sort of small base stations, the application of the idle mode scheme of terminals are as it is may cause some problems. Namely, in case of a terminal, an idle mode of the terminal may be immediately changed from an idle mode to an active mode by a user manipulation or a paging message delivered in a network, but in case of the femto cells, if an operation scheme of the femto cells is changed through a manipulation of the user who uses the femto cells or according to a paging signal through a network, it is difficult to quickly and appropriately cope with the surrounding environment of the femto cells.
Also, when many femto cells operate in the idle mode around, interference between the femto cells in the idle mode may be generated or a terminal cannot receive information of the corresponding femto cells due to the difference in an operational period of the idle mode, causing a problem in that it is difficult to search for a nearby femto cell.